Patent GB-629293-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1946-11-15
Abstract: 629,293. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and HENSLER, B. A. Nov. 15, 1946, No. 33996. [Class 40 (iv)] A selector for making tan. dem connections between trunks (or toll lines) has outlets giving direct access to groups of trunks (or toll lines) and other outlets giving access to a manual board and to local automatic exchange equipment. If the wanted group is operating on a delay basis, the marking circuit for the group is disabled and the call is routed to a manual board. The outlets to the trunks are tested before the outlets to the manual positions which are always marked. A line circuit is provided at each end of a trunk and arrangements are made for both-way working. Through signalling is used between similar trunks in tandem. Loop signalling is used between the terminals of trunks of different types when connected directly over a selector. Leg signalling is used in manual connections. In the example shown, provision is made for the setting up of four-wire switching conditions and for feed control as described in Specification 499,832. A trunk comprises two normal speaking wires marked + and - and two extra speaking wires N+ and N - which are connected to four of the eight banks of a motor-driven uniselector provided with staggered wipers. The selector is controlled by a marker switch with contact banks M1 to M5, crossconnections being made between the bank M4 and the bank M of the selector. The selector is prepositioned for digits exceeding a predetermined value. Voice frequency signals on two frequencies X, Y operate receivers (not shown), connected to wires WSR, the contacts x, y being operated by the respective receivers. Similar voice frequency signals are transmitted from wires WSX, WSY under control of relays TX, TY which operate in series with winding III of relay SP, the signals being applied to the trunk over sp3, sp6. Call incoming over trunk. The pick-up signal comprising a short pulse of X-frequency closes contact x and operates a call holding relay B followered by BR, BA and CB. Relay CB grounds the " P " wire at cb5 to mark the trunk busy for calls outgoing in the reverse direction and operates at cb1 a traffic recorder connected to terminal IC. The stepping magnet DM of the marker switch is advanced by the pick-up signal and by the impulses of the first digit which follow. Dialling relay C falls back at the end of the impulse train to start the selector driving mechanism over c7. The selector stops when it seizes a free line in the marked group, TA testing over marker bank M4, selector bank M, contacts c3, ba4 and bank P. Test relay TA is followed by relays S, SA to switch the trunk through to the seized outlet. If the first digit exceeds a predetermined value, the selector is started before the marking switch stops, contact c7 being omitted from the corresponding selector driving circuits. If the selector reaches a control position in which the first-to-enter wipers engage the penultimate contacts of their banks before dialling relay C falls back, the switch is stopped temporarily by the operation of relay TA over contact c3 and resistance YA and starts again when c3 falls back. The impulses of further digits are repeated by relay A, contacts s in the speaking wires now being closed. Reply of the called party is signalled by current reversal which operates a back-bridge relay D followed by relays TY, SP to repeat the answer signal as Y-frequency pulses, TY being connected to interrupted earth at WEA. An answeracknowledgement signal comprising a pulse of Y-frequency so timed that it is received between answer pulses operates contact y, followed by relay G which cuts-off the answer signal at contact g5. Operation of contact y also brings about the slow release of relay Z and the operation of answer-received relay AR. As the pulse ends, relay Z operates again before ZR falls back and relay SP is released to complete the through connection at sp3, sp6. When the called party clears, back-bridge relay D is released by current reversal and relays SP and TY operate to transmit the clear back signal as pulses of Y-frequency. When the calling party clears, a clear forward signal is transmitted as a long application of Y-frequency, allowing G to operate and both Z and ZR, to release to operate control relays FL, AT and to release holding relay B followed by BR, S, SA and TA. At the termination of the clear forward signal a release signal consisting of a pulse of Y-frequency is sent back by TY. Relays FL, AT fall back to complete a self-interrupting homing circuit for the marker at at3 and the release signal terminates when BA falls back. Delay working. Contacts of marker bank MS corresponding to trunks available directly are grounded through a total call meter in series with which relay DL does not operate. When a trunk is operated on a delay basis, the M5 contact is directly grounded and operates DL when tested. The marking circuit over bank M4 is disabled at dl2 and the selector is driven to the manual outlets which are tested over rt3 and terminal TEM which is cross-connected over bank M and contacts c3, ba4 to bank P. On reply of the operator, a relay AS is operated over the " S " wire and is followed by SB, which holds A, AX, AY and prepares the back bridge circuit for through signalling. On reply of the called party, back bridge relay D is operated by battery on the positive speaking wire and both answer and answer-acknowledgement signals pass as before. The clear back signal is transmitted as before when the called party clears. A ring forward or re-call signal takes the form of a long pulse of X-frequency which operates XA over sb7. For the period of the signal, Z releases and SP operates to repeat the signal to a distant exchange by applying battery to the negative speaking wire over resistance YF. At the same time, AR releases and RC operates to apply interrupted earth from WEC to the " S " wire to flash the supervisory lamp at the operator's position. When the operator answers the re-call signal, the resistance of the '' S '' wire is reduced to operate AS, thereby releasing RC and extinguishing the supervisory lamp signal. Call outgoing over trunk from line circuit. The leads shown at the top of Fig. 2 are connected to an outlet of a selector. When the trunk is tested over the " P " wire, call holding relay GS operates and is followed immediately by AX, AY and, after a delay, by GT. For the period of the delay SP and TX operate to dispatch the pick-up signal to the incoming end of the trunk as a short pulse of X-frequency. Relays HB(i), SB(ii) and SA, together follow GT, SB setting up conditions for through signalling. When BA, CB and Z follow, the circuit is ready to receive dialled X-frequency impulses which are passed on without repetition. When the called party replies, the answer signal, in the form of a pulse of Y- frequency, leads to the operation of AT and AR(ii) after the operation and release of ZR and the connection of battery over resistance YA to the positive speaking wire to operate the back-bridge relay D in the preceding line circuit. When the answer signal ends, y falls back, Z and ZR operate and SP releases and re-operates in series with TY over at5 to transmit the answer-acknowledgement signal as a pulse of Y-frequency during the delay before AT falls back. When the preceding line circuit clears and ground is removed from the " P " wire, GS releases, but meantime keeps the line busy by grounding the " P " wire over cb5. Relays A, AX, AY release and GT(ii), TY, SP(iii) operate in series to transmit the clear forward signal as a pulse of Y-frequency. Interrupted earth from WEB steps the marker switch from normal to the fifth position, where SP and TY are released to terminate the clear forward signal. The line circuit is returned to normal in response to a release signal of Y- frequency, the marker being self-stepped in two stages, from the fifth to the ninth positions before and from the ninth position to home after GT falls back. If battery is applied to the negative speaking wire in a preceding circuit to give a ring forward or re-call signal RF operates on winding (i) and holds on winding (ii) for at least a period determined by the condenser QA. During this period TX and SP operate over rf1 to relay the re-call signal as a pulse of X-frequency and AR is released in preparation for the transmission of an answer-acknowledgement signal. Transit signalling. By operation of relay TT, over the TT wiper of the selector, the circuit is conditioned to respond only to the clear forward signal which brings about the release of the circuit. Relays BR, S and SA are held for the duration of the clear forward signal so that the signal is transmitted forward to the succeeding trunk line. Unidirectional working may be established by means of a key O/G for outgoing calls and a key I/C for incoming calls. The trunk can be shut down by means of a key KS. Terminal OG and GC give access to traffic recording and group control circuits. Relays FW, PC and PCA are part of the feed control arrangement.